It is not known when Mozart completed this concerto for two pianos in E-flat major, K. 365/316a, but research by Alan Tyson shows that cadenzas for the first and third movements are written in his and his father's handwriting on a type of paper used between August 1775 and January 1777. It is presumed that Mozart wrote it to play with his sister Maria Anna (“Nannerl”). Years later he performed it in a private concert with pupil Josepha Barbara von Auernhammer. The above text from the Wikipedia article "Piano Concerto No. 10 (Mozart)" text is available under CC BY-SA 3.0.